Our studies have demonstrated differential effects of immune reactions on normal and malignant epidermal cells, respectively. These reactions result in resolution of skin cancers with minimal or no detectable effects on normal epidermis. We therefore propose to investigate: 1. Factors responsible for the difference in the intensities of immune reactions affecting normal and malignant epidermal cells. 2. Studies on the effects of immune reactions on neoplasms. The eventual goal is to determine whether immune reactions affecting normal and malignant epidermis can be developed into a model system which may yield further information on fundamental aspects of immunology, tumor biology and their relation to host defense mechanisms.